A tilting pad bearing and a thrust pad bearing, each of which configures the bearing surface with multiple independent bearing pads, have an advantage of rapidly absorbing vibration of rotating shafts. Due to this advantage, bearings of these types have been broadly applied to rotating machine, such as a steam turbine and a gas turbine. In recent years, such rotating machine has cherished heightening of the output and lowering of the loss than ever. For this purpose, bearing loss needs to be suppressed by reducing the size of the bearing that bears the rotating shaft of the rotating machine. However, it is sure that a small bearing can suppress bearing loss, but the resultant small pressed area of the bearing increases the bearing load (weight on the bearing per unit area) to raise the temperature of the bearing pads.
While the rotating machine is working, the lubricant oil between the rotating shaft and the pads evolves heat generated by shear force, and each bearing pad, if being a journal bearing, becomes hotter towards the inner surface close to the rotating shaft and becomes also hotter towards the downstream of the rotating direction of the rotating shaft. This means that the bearing pad has an inner temperature difference and would become deformed due to differential expansion (differential thermal expansion). For example, in a tilting pad journal bearing, when each tilting pad becomes hotter at a portion closer to the inner circumference side nearer to the rotating shaft and thereby has an internal temperature difference between the inner circumference side and the outer circumference side, the tilting pad becomes deformed so as to increase the radius of curvature opposing to the rotating shaft, so that the bearing has a degraded capability of dealing with load.
Specifically, the tilting pad journal bearing has tilting pads each of which has an inner circumference surface (supporting surface) opposing to the outer circumference surface (supported surface) of the rotating shaft, and a lubricant oil film is formed at a space between the opposing surfaces. The presence of the lubricant oil film enables the bearing to smoothly support the rotating shaft.
If a tilting pad undergoes thermal deformation to have an increased radius of curvature, the space is widened more than needed at the inlet and exit portions to make it impossible to retain the oil film. For this reason, the oil film is entirely thinner. However, a thin lubricant oil further evolves heat.
Consequently, the temperature of the entire tilting pad is elevated to further deform the tilting pad, and finally, the bearing comes into contact with the rotating shaft (so that the bearing becomes incapable of loading the rotating shaft). Accordingly, the bearing has a degraded capability of dealing with the load.
Furthermore, deformation of a tilting pad affects the dynamic stability of the tilting pad. Namely, the attenuation coefficient lowers and therefore the tilting pad fails to rapidly absorb the vibration of the rotating shaft.
As a solution to the above, there is proposed a technique of forming a conduit penetrating the bearing pad from the front end surface to the rear end surface and cooling the entire bearing pad by a low-temperature additional oil flowing through the conduit (see Japanese Patent Publication No. 2009-063015, hereinafter “JP 2009-063015”).
As another solution, there is provided a technique of suppressing deformation caused by internal temperature difference by using material having a high thermal conductivity, such as Chromium copper.